IANA time zone database

The tz database, also called tzdata, the zoneinfo database or IANA (Internet Assigned Numbers Authority) time zone database, is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. It is sometimes called the Olson database, referring to the founding contributor, Arthur David Olson. Paul Eggert is currently^[update] its editor and maintainer.

Its uniform naming convention for time zones, such as America/New_York and Europe/Paris, was designed by Paul Eggert. The database attempts to record historical time zones and all civil changes since 1970, the Unix time epoch. It also includes transitions such as daylight saving time, and also records leap seconds.

The database, as well as some reference source code, is in the public domain. New editions of the database and code are published as changes warrant, usually several times per year.

The tz database is published as a set of text files which list the rules and zone transitions in a human-readable format. For use, these text files are compiled into a set of platform-independent binary files—one per time zone. The reference source code includes such a compiler called zic (zone information compiler), as well as code to read those files and use them in standard application programming interfaces such as localtime() and mktime().

Within the tz database, a time zone is any national region where local clocks have all agreed since 1970. This definition concerns itself first with geographic areas which have had consistent local clocks. This is different from other definitions which concern themselves with consistent offsets from a prime meridian. Therefore, each of the time zones defined by the tz database may document multiple offsets from UTC, typically including both standard time and daylight saving time.

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